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Why the whitness of two- sides are difference?
1.Due to the fourdrinier paper machine has a machinery problem itself, the Z-direction distributing of filler and tiny fibril is inequable, so the two-sidedness is largest. If the retention is poor, that will increase the difference between two sides more greatly.
2. The difference of affinity to bleaching chemical pulp and filler between direct dye and FWA s is large, that makes great difference in CIE whiteness and ISO whiteness.
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Why the hue of paper changes greatly when the whiteness decreases?
With the whiteness decreasing, the value of L, a, b changes greatly, the hue of paper varies with a trend to dark, yellow and green.
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Why are there some color spots in the paper?
1. If it is color point, that maybe from the decomposition product of bacteria or mixed impurity.
2. If it is colored Fibrous substance, that has relationship to the fiber and dye. If the content of lignin is high, that should pay attention to the adding method of direct dye and basic blue, partial overhigh concentration or dead space of approach flow system, which also make partial fiber dye excessively.
3. On the effect of poor paper uniformity，high color saturation，there maybe looks like some color spots in the paper
4. When dye is added in the surface sizing, color spots are maybe produced because of unevenness of sizing roll or uniformity of sizing. As it is difficulty to solve, the dye is not advised to add in the sizing.
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Why dose the paper color look differently in daytime and evening?
The difference between sunlight and the light of common lamp is large. The incident light have affect on the reflected light. So the paper color looks changing a lot in different light.
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Why sometimes anionic direct dye is difficulty to colorize and the colorizing result is insensitive to dosage?
1. The PCD of the system is too negative;
2. The free activity hydroxy in the fiber is held by other chemical molecule;
3. The anionic of the dye is too high, and the binding capacity to fiber is low.
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Why the kinds of pulp and FWA are not changed, but the FWA dosage of each ton paper increases evidently?
The proportion of pulp and chemical, FWA are the important factors which influence the whiteness of paper, the conditions of papermaking process influences the dosage of FWA as well, especially the control of recovery rate of whitewater is very important. The first-past retention of FWA added into the pulp is always not high, that is far lower than the total retention to the papermaking machine. So if large amount of whitewater is not recycled, this will make the huge loss of FWA.
In addition, there are a lot of factors influencing the efficiency of FWA, such as residual oxidative substance (residual chlorine, strong oxidative bactericide) from the bleaching pulp, water(containing heavy metal ion, rot bacterium), the kind and dosage of other cationic substances, addition point, pH value, the kind and dosage of dye and filler, papermaking process(the beating degree , paper machine speed, the change of moisture in the process of papermaking, press pressure) and so on.
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The weather resistance of paper is poor and the whiteness declines rapidly. Why?
1、Yellowing of paper mainly comes from lignin. High content of lignin is a great factor. But there are many other factors which can affect the lignin yellowing.
①→pH value. Higher or lower pH value can decrease the whiteness rapidly. So the neutrality is the best.
②→Metal ions. Ferric ion is the catalyst for light induced yellowing of lignin.
③→Pulping and bleaching. The weather resistance is better when using hydrogen peroxide in bleaching than using hypochlorite. How to increase the weather resistance of paper by pulping, bleaching and additive is a big project.
④→Adding useful additive. For example, FWA can snatch ultraviolet from lignin and decrease the light induced yellowing. Antioxidant can help the lignin avoid oxidation, etc.
2、Poor quality or inappropriate type of FWA and dye can also decrease the weather resistance.
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Why is whiteness different between the internal and the external of a paper roll?
1、Temperature has effect on whiteness. After winding paper, the temperature of internal paper roll is higher than external, so the whiteness of internal paper roll is lower, especially to those papers which have a high content of lignin.
2、The abnormal running condition can also affect the whiteness. For example, the dosage of FWA is not adjusted in time when the proportion of defective paper fluctuates greatly and rapidly.
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Why does the replacement of FWA cause the problems such as deposit appearing, paper defect increasing, operation efficiency decreasing?
Due to the differences in processing technique, raw materials and formulas, the final product components (including minor metal ions etc..) of different FWA or the same type FWA from different manufacturers are often different. So the compatibility between FWA and other paper chemicals is different. Then, although with the same name of FWA type, if there are problems happened in compatibility, it will affect the operation efficiency of paper machine even make the deposit occur which will cause paper defects.
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Why is the paper hue somewhat greener while the dosage of FWA is not large?
Generally speaking, the greener hue means yellowing in advance.
1、There have already been many FWAs in raw materials(waste paper).
2、The FWA has quality problem.
3、There are acidic matters in the system which lower the pH value.
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Why is the visual whiteness good but tested whiteness somewhat lower?
Many paper mills are still using ISO single whiteness index to evaluate the paper whiteness. This whiteness index is only related to the whiteness of raw material and the fluorescent whiteness of FWA. All dark color (such as blue-violet dyestuff) paper chemicals will decrease the base whiteness of paper furnish. But the visual whiteness by naked eye is also related to chromatic light of paper. Within certain color saturation, blue-violet hue paper looks much whiter which shows in the way that the visual whiteness is positive related to the CIE whiteness.
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Why does the retention decline after replacement of the FWA?
1、During the synthesis process of FWA, all the main products and by-products are anion substance. This is equivalent to provide anionic trash to the wet end.
2、 Sodium chloride (salt) is one of the products in the synthesis process of FWA. But in some synthesis process of solid FWA, salt is often added in, which will greatly increase the electrical conductivity of the closed wet end system. Furthermore, it will affect the efficacy of the cationic polyacrylae retention additives.
